Over the past few years, microfilm has seen increasing use as a medium of choice for compactly storing extremely large amounts of document information. Conventionally, this form of storage relies on optically reducing the size of a page by a substantial amount and then photographically capturing an image of the reduced page on a corresponding frame of microfilm. Each such photographed page may depict a page in a periodical or the like or simply an individual business record, such as a completed business form or the like. Microfilm itself generally takes the form of a roll of developed film that frequently contains a transparency in the form of a strip that contains thousands of successive images all substantially reduced in size.
To read a microfilm image, through for example a manual film reader, an operator first obtains a roll of microfilm that contains the desired image. The operator then inserts that roll into the film reader and then advances a film transport mechanism in the reader to thread an end of the film onto a suitable motor driven take up spool. Once this has occurred, the operator advances the drive mechanism, typically by appropriately turning a control dial to increase the speed of the take up spool to advance the film in a serial fashion until the desired image appears on the screen of the reader. When the desired image is reached, the operator stops the movement of the film, inspects the image, and then often instructs the reader to print a full size hard copy reproduction of the image for later use.
In view of the continuing recognition in the art that microfilm provides an excellent medium for large scale storage of substantial amounts of documentary information, the art is increasing turning to the use of image management systems in an effort to automate the document retrieval process. Such systems are aimed at not only providing an increased throughput of retrieved documents but also providing various capabilities to electronically print and process each retrieved image, such as through image enhancement, rotation, annotation, and the like. In such a system, the same basic sequential process that occurs with a manual reader is used, though in an automated fashion. In particular, a typical image management system incorporates a computer which contains a stored database that possesses an entry (record) for each microfilmed document (microfilm image) stored on the system. For each such document, its corresponding entry contains identifying indicia, such as an abstract or title, of that document and an accompanying microfilm roll and frame number at which an image of that document is stored. Once an operator selects an appropriate document by conducting an on-line computerized search of the database, the computer performs an appropriate database access operation into the record for that document to determine its corresponding roll and frame number. Thereafter, the computer instructs an automated microfilm reader, i.e. a so-called film library also frequently referred to as an "autoloader", to physically retrieve the corresponding roll of microfilm, place it within the reader and then automatically advance the film in that roll until the image of the desired document is reached. Once this image is reached, the reader then electronically scans the image to produce a digitized grey scale representation of the stored document. The digitized image is applied to a local area network to be routed to downstream equipment for storage; image processing, such as enhancement, rotation and/or annotation; display on a video terminal and/or printing.
Oftentimes, a problem frequently occurs with a microfilm based document retrieval system. Specifically, once a roll of microfilm has been advanced to what the operator thought was the proper frame, a wrong document appears on a display screen. In a manual microfilm reader, this problem frequently occurs, because the operator may have simply loaded the wrong roll of microfilm, i.e. a roll that did not contain the desired document, into the reader. The same problem occurs in an image management system if the operator selected the wrong record from the data base or if what was believed to be the correct record actually contains an erroneous entry, i.e. a wrong roll or frame number or document description.
As such, when a wrong document is encountered, the operator of a manual reader will generally attempt to search the roll that exists in the reader in an attempt to locate the particular frame that contains the desired document. Such a search operation, hereinafter referred to as a search mode, frequently involves advancing the microfilm at a relatively fast speed which permits the operator to obtain a very quick glimpse of a full sized image of each document as images of successive frames are sequentially displayed on a display screen of the reader. In this mode of operation, the film is initially advanced at a high speed until the operator believes he or she has reached a section of the film that is likely to contain the desired image at which point the operator appreciably decreases the film advance speed in order to accurately inspect each individual successive frame in that section as it moves past the viewer. Once the desired image is reached, the film advance is terminated. An operator will also undertake a search operation when examination of one document reveals the need for additional information that may be contained in other documents that are stored on nearby prior or succeeding frames of the same roll.
As such, microfilm based retrieval systems need to accommodate a search mode. This can be readily accommodated in a manual reader by merely providing a control that permits an operator to manually vary, i.e. increase or decrease, the speed of the film transport mechanism while successive full sized document images are optically and simultaneously projected on the display screen of the reader.
Unfortunately, providing a search mode is considerably more difficult to implement in an image management system than in a manual reader. Specifically, the optics in a manual reader respond significantly faster than the human eye. As such, the limitation on the speed at which a search mode can be undertaken in a manual reader lies with the operator rather than with the reader itself. By contrast, each microfilm frame that is to be displayed by an image management system must first be electronically scanned into a frame store memory the contents of which, when filled, are then transmitted often in a compressed form over a local area network to a video processor that decompresses the image for subsequent display on a terminal. All these operations impart a finite lag into the response of the system as contrasted with the instantaneous response of the projection optics in a manual reader. To reduce the lag, pipelined operation can occur in which one image is being scanned while all the other operations are occurring for one or more of the images that were just previously scanned in sequence. Unfortunately, image management systems typically utilize a charge coupled device (CCD) imager which requires a finite period of time, the so-called integration time, to provide a satisfactory response for each scanned line. It is principally the integration time that appears to limit the rate at which successive microfilm images can be scanned. For example, assume that the fastest search mode would require the display of 10 successive full sized images/second with a reasonable search mode requiring the display of 5 full sized images/second. In general, a human eye is incapable of distinguishing different images at a rate much in excess of 10 images/second, if that fast. Hence, if a typical microfilm image contains 1000 horizontal scan lines with 4000 pixels/line, then the CCD imager would need to produce output data at a rate of 40M pixels/second to achieve a throughput of 10 images/second. This rate greatly exceeds the pixel clock rate, typically 10 MHz, at which currently available CCD imagers are capable of operating. If the data rate were to be slowed to 10 MHz, then this would limit the search mode to only 2.5 successive images/second which in many instances is simply too slow to allow for an effective search mode.
Although the art does teach various techniques for scanning continuously moving film, particularly for use in a motion picture film to video transfer operation such as that disclosed in U.S. Pat. No. 4,310,856 (issued to D. Poetsch on Jan. 12, 1982); U.S. Pat. No. 4,268,865 (issued to J. Millward on May 19, 1981); U.S. Pat. No. 4,266,246 (issued to C. Waldron et al on May 5, 1981) and U.S. Pat. No. 4,205,337 (issued to J. Millward on May 27, 1980), none of these techniques appears to operate at a sufficiently high resolution required for a microfilm based image management system.
Therefore, a need exists in the art for a technique, particularly one suited for use in an image management system, that permits a succession of full sized microfilm images to be sequentially scanned while the microfilm is moving at a user adjustable speed so as to produce a suitable number of, e.g. upwards of ten, successive full sized images/second on a display screen. Such a technique could be used to advantageously implement a search mode within a microfilm based image management system.